The BGS Lexicon of Named Rock Units — Result Details

Broadford Beds Formation

Computer Code: BFB Preferred Map Code: BfB
Status Code: Pending Upgrade
Age range: Hettangian Age (JH) — Sinemurian Age (JS)
Lithological Description: The Broadford Beds Formation is fully described by Morton and Hudson, 1995, though Hesselbo et al, (1998) contradict this and rename the units described. BGS maps are based on the former reference. The description includes BHLS, BRKH and ADS, which are also documented in the Lexicon. The lower Broadford Beds are dominated by carbonate rocks, calcareous mudstones and mature sandstones. Coral-rich beds are abundant in the lowermost parts and are overlain by restricted marine-fauna-rich lagoonal sediments. A shallowing of marine conditions from neritic deposition during Blue Lias times to nearshore/lagoonal is inferred. The upper Broadford Beds comprise sandstones and sandy siltstones. Typically these are highly micaceous and ferriginous. An ironstone bed with chamosite is found on the Ardnish Peninsula. A diverse marine faunal assemblage is common.
Definition of Lower Boundary: Transitional, transgressive mudstones and sandstones from underlying Triassic.
Definition of Upper Boundary: Abrupt facies change to Pabay Shale Formation.
Thickness: 50 to 100m
Geographical Limits: Sea of Hebrides Basin.
Parent Unit: Lias Group (LI)
Previous Name(s): UPPER BROADFORD BEDS
LOWER BROADFORD BEDS
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Hallaig, Isle of Raasay - both Lower and Upper Broadford Beds reference section. 
Reference Section  Ardnish Peninsula, Broadford Bay, Isle of Skye - lower beds at Ob Lusa, upper beds on the northern margin of the peninsula. 
Reference(s):
Morton, N and Hudson, J D, 1995. Field Guide to the Jurassic of the Isles of Raasay and Skye, Inner Hebrides, north-west Scotland. In: Taylor, P D (editor), Field Geology of the British Jurassic. Geological Society of London, 209-280. 
Morton, N. 1965. The Bearrenaig Sandstone Series (Middle Jurassic) of Skye and Raasay. Scottish Journal of Geology, Vol.1, 189-216. 
Fyfe, J A, Long, D and Evans, D, 1993. United Kingdom offshore regional report: the geology of the Malin - Hebrides sea area (London: HMSO for the British Geological Survey). 
Hesselbo, S P, Oates, M J and Jenkyns, H C. 19998. The Lower Lias Group of the Bebrides Basin. Scottish Journal of Geology, Vol.34, Part 1, 23-60. 
Morton, N 1999. Middle Hettangian (Lower Jurassic) ammonites from the Isle of Raasay, Inner Hebrides, and correlation of the Hettangian - lowermost Sinemurian Breakish Formation in the Skye area, north-western Scotland. Scottish Journal of Geology. 
Cox, B M, Page, K N and Morton, N, 2002. The Middle Jurassic stratigraphy of Scotland. In Cox, B M and Sumbler, M G (editors), British Middle Jurassic Stratigraphy. Geological Conservation Review Series, Vol.26. (Peterborough: Joint Nature Conservation Committee/Chapman and Hall.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S071 S071 S081 S043 S044 S043 S044 S051 S070 S060